1. Field of the Invention
The present invention relates to a cordierite honeycomb structure and more particularly to a cordierite honeycomb structure used as a catalyst carrier of converters for the purification of exhaust gases and a process for producing the same.
2. Description of Related Art
At the present time, in converters for the purification of exhaust gases discharged from automobiles and the like, cordierite honeycomb structures are used as a carrier on which a catalyst is supported.
In recent years, the demand for the purification of exhaust gases discharged from automobiles and the like has become strong. In order to meet this demand, an improvement in conversion efficiency through rapid activation of the catalyst has been required of the converters.
For this reason, an attempt to activate the catalyst supported on the carrier as quick as possible has hitherto been made in order to improve the conversion efficiency.
Initial conversion efficiencies in a transient state in addition to conversion efficiencies in a steady state are very important to the early activation of the catalyst in the converters, for the purification of an exhaust gas, used in automobiles. For example, the early activation of the catalyst which minimizes the time taken for the conversion efficiencies of the catalyst to reach the contemplated ordinary level is related to an improvement in the overall conversion efficiencies.
For this reason, various proposals have been made on the rapid activation of the catalyst.
For example, in Japanese Examined Patent Publication (Kokoku) No. 4-37028, in order to realize rapid activation of the catalyst by exposing a catalyst carrier to an exhaust gas at a high temperature in such a manner that the catalyst carrier is disposed in the vicinity of the engine, a honeycomb structure of cordierite having a coefficient of thermal expansion attributable to a porosity of not more than 30% has been proposed to improve the thermal shock resistance of the catalyst carrier to such an extent that the carrier per se causes neither cracking nor other unfavorable phenomena upon rapid temperature rise of the carrier per se.
Further, regarding the thermal shock resistance, Japanese Examined Patent Publication (Kokoku) No. 2-12898 proposes a cordierite honeycomb structure having a pore diameter and a pore volume attributable to a porosity of less than 25%.
As described above, in the rapid activation of the catalyst in the prior art, cordierite ceramic bodies have been studied with the focus placed on the thermal shock resistance, and no satisfactory rapid activation of the catalyst have been achieved yet.